The present invention relates to fiberscopes. More particularly, the invention relates to a fiberscope for optically observing a region filled with opaque liquid such as the inside of a blood vessel or the heart.
FIGS. 1 and 2 are explanatory diagrams showing a conventional fiberscope. A flexible tube 1 includes illuminating light transmitting light guides and an image fiber for directly transmitting an image. The former is coupled to an illuminating light source 3, and the latter is coupled through an image receiving adapter 2 to a light-receiving unit such as a 16-mm movie camera or a television camera.
More specifically, the flexible tube 1 encases light guides 9 for transmitting illuminating light from a light source 3 to a region 5 to be observed (the inside of a blood vessel 7 as shown in FIG. 2), an image transmitting image fiber 11 having at the forward end thereof a lens for forming the image of an object, and a liquid guide passage for introducing a physiological saline solution from a syringe 13 to the observation region 5 in front of the light guides 9 and the image forming lens of the image fiber 11 to form a transparent region. In order to provide the transparent physiological saline region in the flow of blood as described above, it is necessary to eject the saline solution from the end of the fiberscope at a flow rate at least substantially equal to that of the blood at that point, typically, about 50 cm.sup.3 /sec.
FIG. 3 shows a cross-sectional view of the flexible tube in a conventional fiberscope. A liquid guide passageway 15 having a circular cross section is disposed between a tube 1 and light guides 9, which also have circular cross sections. In this case, the outside diameter of the tube 1 is necessarily limited (4 mm for instance), and accordingly it is impossible to increase the effective cross-sectional area of the liquid guide passage 15 through which the saline solution passes, and hence it is also impossible in many instances to inject the saline solution at a sufficiently high flow rate.
A transparent region may be formed at the front end of the fiberscope by employing, instead of a flush of physiological saline, a transparent balloon attached to the front end of the fiberscope which is inflated for observation. However, this technique suffers from the drawback that the flow of blood is stopped in a small diameter blood vessel.
FIG. 4 shows a cross-sectional view of another example of a conventional fiberscope. In this conventional fiberscope, a fiber bundle 12 includes light guides 9 and an image fiber 11, and the liquid guide passage 15 is provided between the tube 1 and an outer peripheral surface of the fiber bundle 12. With this structure, the cross-sectional area of the liquid guide passage 15 is larger than that of the first conventional example shown in FIG. 3. However, the effective cross-sectional area is still limited due to the limitation of the outer diameter of the tube 1. Therefore, a sufficient flush may not be obtainable as in the first conventional example.
Further, in the fiberscope, in order to separate the liquid guide passageway 15, which communicates with the syringe 13, from the fiber bundle 12, including the light guides 9 coupled to an image pickup unit 4 and the image fiber 11, a branching section 19 is provided at the rear end of the tube. The structure of the conventional branching section is as shown in FIG. 5. A small hole 21 is formed in the wall of the flexible tube 1, and the fiber bundle 12, including the light guides 9 and the image fiber 11, extends through the small hole 21. The small hole is covered with a silicon resin layer 23 formed by coating, and an epoxy resin layer 25 is molded over the silicon resin layer. Then, the tube 1, the silicon resin layer, and the epoxy resin layer are wrapped with a tape 27.
This structure of the conventional branching section is disadvantageous in the following points:
(1) Since the flexible tube 1 in which is formed the small hole 21 is soft, the position of the small hole is unstable during the resin coating and molding process and in wrapping the tube with tape, as a result of which the sealing effect is liable to be unsatisfactory.
(2) Since the resin molding proccess, or the tape wrapping operation, takes a relatively long time, the manufacturing cost is high.
(3) At the branching section, the fiber bundle 12 is supported by the soft flexible tube 1, and hence it is not sufficiently stiff.
(4) The outermost layer of the branching section is formed by manually wrapping the tube, the silicon resin layer and the epoxy resin layer with tape. Therefore, the external appearance of the branching section is poor.
An improvement to obtain a sufficient amount of flushing solution is disclosed in commonly assigned copending U.S. application Ser. No. 561,705, filed Dec. 15, 1983.
FIGS. 6-10 shows the fiberscope described in the copending application. The blood vessel insertion section of the fiberscope includes a flexible tube 1 housing a fiber bundle 12' composed of an image fiber 11, having a lens for forming the image of the object under observation at its front end, and light guides 9. A liquid guide passageway 15a for introducing physiological saline solution is formed between the inner wall of the cover tube 1 and the outer wall of the fiber bundle 12'. The fiber bundle 12' is formed by bundling the image fiber 11 and the light guides 9 with a thin binding thread or tape 6 and then wrapping them with small bands 8 made of a heat-shrinkable material. The fiber bundle 12' thus formed is loosely inserted into the cover tube 1, except for an area near its front end portion. A cap 10 is provided at the end of the fiberscope to hold the fiber bundle 12' in the cover tube 1 in such a manner that the fiber bundle is held coaxial with the cover tube. The cap 10, as shown in FIGS. 9 and 10, is composed of a sleeve 13 for holding the front end portion of the fiber bundle 12', spacers 14 provided at equal intervals around the sleeve and bonded to the inner wall of the cover tube so that the sleeve is held coaxial with the cover tube, a concave front wall 16 extending inwardly from the front end of the sleeve 13 and bonded at its periphery to the inner wall of the cover tube 1, and outlets 16a formed in the front wall 16 to communicate with the liquid guide passage 15a. The inner surface of the front wall 16, as shown in FIG. 10, is formed as a guide wall for directing (as indicated by an arrow), on the upstream side of the outlets 16a, the flow of saline from the liquid guide passage 15a towards the front end face of the fiber bundle 12', that is, towards the lens at the front end of the image fiber 11 and the front end faces of the light guides 9.
With this structure, a large cross-sectional area of the liquid guide passage can be obtained within a limited space. However, the fiberscope thus constructed is still disadvantageous in the following points:
(1) In order to increase the flow rate of physiological saline solution, the pressure used for injecting the solution is necessarily high.
(2) For the same purpose, the outside diameter of the flexible cable is large, and accordingly the applications where the fiberscope can be employed are limited.
(3) Because of the large flow rate and large volume of flow of the physiological saline solution, adjacent tissues may be damaged.
(4) The cap 10 used for positioning the fiber bundle 12' in the cover tube 1 in such a manner that the fiber bundle is held coaxial with the cover tube 1 has a considerably intricate structure to prevent as much as possible obstruction of the flow of saline solution. Therefore, the manufacturing cost of the cap 10 is necessarily high. Specifically, since the cap 10 is of a small size and must be produced by machining and molding, the production cost of the cap is high, thus making the manufacturing cost of the resultant fiberscope high.
(5) The contact area of the cap 10 and the cover tube 1 cannot be made as large as is desirable because of the cap structure. Therefore, the cap is not sufficiently bonded to the cover tube, and it may be dislodged from the tube by shocks which occur during flushes of physiological saline.
(6) Since the structure of the cap 10 is intricate as described above, it is difficult to provide a cap of small size. Accordingly, the outside diameter of the cover tube 1 is large, and therefore it is difficult to insert it into a blood vessel.